Refactore slug API for generating tag and post slugs.

Closes #2601
- Removed slug generation from the post API
- Added new, self-contained slug API
- Fixed slug permissions in the fixtures files
- Added a HTTP route for the new API method
- Added integrational tests
Fix up url helper unit tests

Closes #2817
-use async semantics for tests
-fix api.settings.read stub for the url helper describe block
-rename test to describe actual behavior (return '/' instead of '')
Merge pull request #2818 from jaswilli/issue-2817

Fix up url helper unit tests
Merge pull request #2814 from lennerd/issue-2601

Refactore slug API for generating tag and post slugs
Ember Data with Posts

Ref #2699

- Introduce ember data dependency
- Add loadInitializers and refactor most initializers into one combined
- Add Post ember data model
- Refactor generateSlug to use title of post and ghostPaths
- Refactor post controller to not reference model.property everywhere
- Use RESTAdapter for posts, users and tags
- Setup author and tag relations in Post model
- Fix broken API calls by adding CSRF header
- Add initiaizer for csrf value
- Use actual User model for current user initializer
- Add action for setting featured post, test with actual api call
- Fix the sending of UUID's up to the server
- Refactor current-user to use ember-data store
- If a user is preloaded in the application, use pushPayload to put it
in the store
- Do a lookup on the store to get an actual User model for injection
- Fix posts/post controllerName in route/new.js
- Alter signup process to push user into ember data store